Joseph Devenney/Getty Images(KAUFMAN, Texas) -- State and federal authorities have upped the reward for information leading to the killers of Texas prosecutor Mark Hasse to $70,000, but said Sunday they do not have a motive or suspects in Thursday's shooting outside the Kaufman County Courthouse.

Authorities confirmed they are combing through past cases handled by the assistant district attorney for a possible motive, but said they knew of no current cases that Hasse had been handling that involved the Aryan Brotherhood of Texas, one of the nation's most violent prison gangs.

Hasse was shot Thursday just before 9 a.m. by one or two unknown assailants as he walked from his car to the courthouse in the small town of Kaufman southeast of Dallas.

The assailants, who may have been masked and dressed in black, fled the scene in a silver four-door sedan. The murder came the same morning that two members of the ABT pleaded guilty to racketeering in a Texas federal court.

On Thursday morning, the Dallas Morning News reported that "authorities with knowledge of the assistant DA's caseload [said] he had been heavily involved in the investigation of members of the Aryan Brotherhood."

The Kaufman County DA's office, where Hasse and a dozen other ADAs worked, was listed as one of 22 agencies on the task force that handled the racketeering case.

In a press conference Friday, Kaufman County Police Chief Chris Albaugh said that it "seems to be a coincidence" that the two events happened on the same morning and called a link between the guilty pleas and the shooting "speculation," but did not rule out the possibility that the shooting was related to one of Hasse's cases.

"We're not ruling out any involvement until we know," Albaugh said. "And we have no specific information that the Aryan Brotherhood is a factor here.

"We are reviewing Mr. Hasse's cases and following up on any leads within those cases that would give us a person of interest," he said.

Hasse, 57, had been a longtime felony prosecutor for the Dallas County District Attorney's Office, according to the ABC's Dallas/Fort Worth affiliate WFAA-TV. He headed the organized crime unit in Dallas in the 1980s. He started work in Kaufman County three years ago.